A new era in skin cancer treatment has been heralded by doctors as they unveiled what has been called the biggest breakthrough in 30 years.

A twice-a-day pill that targets a faulty gene present in melanoma, the deadliest form of skin cancer, has been shown to reduce the risk of death by almost two-thirds in patients with the advanced form of the disease.

James Larkin, of the Royal Marsden Hospital in London, the principal investigator in the UK, said: "This is a pivotal moment. Without question, the results of this trial represent a turning point in the treatment of this disease."

Professor Richard Marais, of the Institute of Cancer Research, who first demonstrated the importance of the gene in melanoma, said: "This is the biggest breakthrough in melanoma treatment in more than 30 years. The results demonstrate that a targeted therapy can work and will change our approach to treating this disease. It is an enormous advance."

The drug is the first "personalised" treatment for melanoma, designed to target cases of the disease which carry the faulty gene, called a BRAF mutation, which account for about half of all cases. As such, it marks a milestone in the transformation of medicines from blunderbuss treatments for everybody to designer drugs tailored to individual cases.

Melanoma has been the fastest rising cancer in the UK over the past 25 years, with more than 11,000 cases a year and 2,000 deaths. It is the second most common cancer in young adults aged 15 to 34 and affects twice as many women as men, although more men die of it. In 2008, malignant melanoma killed 57 people in Northern Ireland, with 297 new cases the same year.

A typical victim is the pale-skinned office worker who spends two weeks broiling on a Mediterranean beach until their skin is red and blistered. Covering up in the midday sun and using high-factor sun cream is the best defence against the cancer.

The drug trial involved 670 patients in the US, Canada, Europe and Australia, including 50 in the UK. It showed survival rates at six months increased from 64% for those on standard chemotherapy to 84% on the new drug, called vemurafenib.